The present invention is in the field of plastic film and especially in the field of films packaged in relatively large rolls.
The invention is particularly related to that film generally referred to as greenhouse film.
Greenhouse film is a type of plastic film made for covering greenhouses or other similar type hot houses used in growing plants and the like. Such film is customarily packaged in large rolls. The film comes in various gauges, but usually has a thickness of about four mils up to six mils. The film ranges in widths from about 10 feet to 50 feet with lengths running from about 50 feet to about 500 feet. Smaller or larger sizes of course, can be made, but are generally not desirable for most commercial uses.
Packaging of film of such gauge, length and width requires a certain amount of folding and rolling to enable the film to be placed in a standard commercial box. The large rolls of film can be difficult to handle and especially when a workman is endeavoring to install same on the roof of a greenhouse.
Greenhouse film is manufactured as an elongated relatively flat tube of a predetermined width and length as well as guage. Sometimes, as circumstances dictate, the film is slit longitudinally on one side so that it might be opened into a single flat sheet of about double the width of the tube.
In packaging greenhouse film, two types of folds have been predominant. One is called a double-fold construction and the other is called a gussetted construction. In the former, a tube of film is folded lengthwise so that one edge is folded over so as to be adjacent the other edge. The film is similarly folded if it has been slit. After folding, the film is rolled into a cylindrically shaped object as is well known in the film rolling art.
In the gussetted construction, each edge of the film is folded inwardly toward the center so as to form a somewhat bellows type tube. The slit film is folded in substantially the same manner. After gussetting, the film is formed into the usual cylindrical roll.
The double-fold construction provides an asymmetrical package. The gussetted construction results in four additional hard folds in the film, which are generally undesirable. This latter type of fold construction also has a tendency to "block".
It is therefore a primary object of the present invention to provide a fold construction for plastic film which is symmetrical.
Another object of the invention is to provide a fold construction for plastic film which does not have hard folds and wherein there is less tendency to "block" since the film is cooled before folding.
Still another object of the instant invention is to provide a package of greenhouse film which permits an installer of the film to center a roll of film on the apex of a roof, unroll the film the length of the greenhouse and then unfold the film to its full width down each side of the greenhouse.